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DESIGNING WITH DOU B LE-TEN ON JOIN ERY Cut the mortises as deep as you can without going all the way through. The deeper you make the mortises, the stronger the joint will be. Minimize the space between the two tenons, but make it wide enough to be cleaned out easily. Use a double mortise-and-tenon joint when strength is an issue, as it is in the freestanding room screen shown above. By doubling the surface area of a glue joint, you can greatly improve its ability to hold together and to withstand stress. will depend on the size of the workpiece. time because it's a safer and quieter machine, and it produces less waste.) When the wood has stabilized, all of the pieces can be rejoimed on two adjoining faces to flatten out any springback that has occurred and then brought down to their final thicknesses with a planer. It's always a good idea to mill some extra stock for setting up the joinery and to use as backups if you make a mistake along the way. With furniture parts that will eventually be sized differently, I prefer to mill all of the stock to the same thickness, complete the joinery and then bring the thinner pieces down to their final sizes with the thickness planer or a handplane. For example, on a conventional table, you can mill the legs and rails first to an equal thickness, then cut your mortises and tenons. After that, send the rail pieces through the planer again to make them thinner and provide a step-back from the surface of the legs when they're joined together. Think through the layout first-I lay out the joinery dimensions for the tenons first. The tenons need to be as long as pos- Photos, this page: Stephen Webster (top left); Michael Pekovich (top right) sible to maintain a strong joint. At this stage, having in hand a good sketch of the joinelY detail is especially helpful. Estimate the amount that each face will be stepped down and then experiment with different tenon sizes until you have a layout that will be strong without creating any weak areas in the joint. I leave the space between the tenons at least a little wider than the narrow ){;-in. chisel that I use to clean up that area. On the outside of both tenons, I'll often leave only a narrow shoulder, about some leeway in deciding the thickness and spacing of the tenons. ){; in. wide, which allows Mark and cut the joinery, starting with the mortises After layout, transfer the width and length of the tenons to the mortise workpieces using a marking knife. If you have to cut more than a few mortises, make a story Tools for multiple marking. A story stick and a marking knife add accuracy and reliability to a repetitive process. MAY / E 2001 43